This invention relates generally to imaging systems, and more particularly, to methods and apparatus for retrospectively assessing image quality of images from imaging systems.
At least one known PET transmission scan is acquired using a rotating source of dual-511 keV gamma rays, such as the Ge-68 rod sources implemented on imaging systems, such as a PET Advance system from General Electric Medical Systems, Waukesha, Wis. During a multiple axial field-of-view (AFOV) study, image quality loss at the end slices of each axial FOV due to lower system sensitivity on these slices may cause an operator to question the overall image quality of the study. This loss of sensitivity is typically corrected by overlapping the axial fields-of-view (AFOVs) by at least one slice of data between two adjacent AFOVs. However, there is often still some degradation in the statistical quality of the overlap slices due to larger patient size (larger patient size typically equals a lower statistical quality), depleting transmission rod source strength, or a shorter transmission scan duration. Often, the attenuation-corrected emission images are viewed in an orthogonal reformat, and a coronal view may show these overlap areas as ‘bands’ of different image quality from surrounding areas. These bands may cause an image reader to question the quality of other areas of the image set. There are several known methods to correct this problem, such as lengthening the transmission scan duration or replacing one or both of the radioactive rod sources. However, often in the clinical setting one can not predict the necessity of pin replacement or probability of occurrence of image quality problems prior to performing the patient scan.